The overall objective of this work is the development of high resolution, real time, three dimensional (3-D) ultrasound imaging systems. The investigators have developed a real time volumetric imaging system currently undergoing in vivo testing. Initial results using a fourth generation phased array system with 256 transmit and 256 receive channels and 16:1 parallel receive processing demonstrate the capability of imaging perfusion defects in the myocardium and providing volumetric data such as left and right ventricular stroke volumes and LV mass in vivo without geometric assumptions. Current image resolution is about 65 cubic mm at 12 cm range, which is barely adequate for clinical applications. In addition, the field of view is limited to a 65-degree pyramid and frame rates are about 20 per second. This application proposes to develop new transmit and receive techniques to further increase the data acquisition rate by a factor of 4 and new higher frequency 2-D arrays to permit a net 10-fold improvement in volume resolution. The staged development of a new generation, high-resolution real time volumetric imaging system based on an earlier engineering testbed is proposed. New concepts in multiple beam transmission and 64:1 receive processing parallelism are to be tested on the modified Duke Phased Array imager which would be upgraded to 550 high speed transmitters and a 250 channel, all digital receive system. Once operational concepts have been verified, the investigators proposed to expand this proof-of-concept system to 1300 transmit and 1300 receive channels for eventual high quality imaging in vivo.